In a dental implant treatment, an easily detachable denture-fixing method comprising fixing a keeper made of a soft-magnetic material to an implant body implanted in the jawbone and magnetically attaching a magnet-containing denture attachment to the keeper is recently used widely.
U.S. Pat. No. 6,709,270 discloses, as shown in FIG. 15, a magnetic dental attachment comprising a keeper 103 made of a soft-magnetic material and threadably engaging an implant body 110, and a denture attachment 105 containing a magnet 155, which is magnetically attached to the keeper 103. The keeper 103 comprises a conically tapered upper portion 135, and a ring portion 137 projecting from an upper peripheral surface of the conically tapered portion 135 and having a circular groove on the rear side. The implant body 110 comprises a conically tapered recess 115 complementary to the tapered portion 135 of the keeper 103. When the keeper 103 threadably engages the implant body 110, a tip end portion of the ring portion 137 of the keeper 103 abuts an upper end portion of the implant body 110, so that tip end portion of the ring portion 137 is elastically deformed radially. Tension generated by this elastic deformation prevents the keeper 103 from loosening. However, because the tip end portion of the ring portion 137 is in contact with the upper end portion of the implant body 110 in a small area in the denture attachment of U.S. Pat. No. 6,709,270, the plastic deformation of the ring portion 137 after a long period of use is likely to decrease the tension, resulting in the loosening of the keeper 110.
JP 2009-131620 A discloses, as shown in FIG. 16, a keeper assembly for an implant comprising (a) an implant body 205; (b) an abutment 204 comprising a head 241 having a female thread 243 and threadably engageable with the implant body 205; (c) a keeper body 202 made of a soft-magnetic material, which comprises a recess 221 for receiving the head 241 of the abutment 204, and a female thread 222 extending along a center axis to have communication with the recess 221; and (d) a screw member 203 threadably engageable with the female thread 222 of the keeper body 202 and the female thread 243 of the abutment 204; the screw member 203 being threadably engaged with the female thread 222 of the keeper body 202 and the female thread 243 of the abutment 204 after the keeper body 202 threadably engages the abutment 204 threadably engaging the implant body 205. However, because the screw member 203 does not have a portion abutting the keeper body 202 or the abutment 204, the axial position of the screw member 203 threadably engaging the keeper body 202 and the abutment 204 should be adjusted manually.
In addition, because the head of the keeper body 202 is as extremely thin as about 1 mm, the female thread 222 of the keeper body 202 has screw ridges only in the minimum number (about 3 or 4) necessary for threadable engagement with the screw member 203. Accordingly, if the threadably engaging position of the screw member 203 were shifted toward the abutment 204, a sufficient fastening strength would not be obtained between the keeper body 202 and the screw member 203. Also, if shifted in an opposite direction, the head of the screw member 203 wound project from the upper surface of the keeper body 202, necessitating the precise manual positioning of the screw member 203.